Marriage look up please

[Galium]

The 1871 census does give Llangenllo as Evan's birthplace, not Aberystwyth.  I think you would need to look for a birth registration in Newcastle in Emlyn district for him. 
If the baptism in Llangynllo is your Evan, then you know he was born before the end of 1867, but as he was only 3 on census night, he will have been born after the end of the March quarter.  So that leaves you with two Evan Davies, one registered in June quarter, and one in December quarter.